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| Name: | CompileMath - converts traditional math to postfix notation | ||
| Synopsis: | string CompileMath -> proc | ||
| Description: |
CompileMath converts a string containing a mathematical expression
in traditional infix notation to a procedure using the
standard postfix notation of SLI. The algorithm is:
1. replace traditonal operators like "-" and "+" with
SLI literals like /sub and /add
2. decompose the string into tokens using the standard
SLI scanner
3. compile the sequence of tokens to a SLI postfix expression
using the predictive recursive-descent parser described in
chapter 2 of the Dragon Book.
The result is the unevaluated expression. This enables the user
to store the expression for later reevaluation.
| ||
| Parameters: | string, is the mathematical expression proc, is the unevaluated expression in SLI postfix notation | ||
| Examples: |
( 5 + 3 * 7 ) CompileMath exec --> 26
( 5 * (3 + 7) ) CompileMath exec --> 50
( 5 + x * 7 ) CompileMath --> {5 x 7 mul add}
( 3 + exp 5 ) CompileMath --> {3 5 exp add}
( 3 + exp ( x ) ) CompileMath --> {3 x exp add}
( 3 + exp ( -x ) ) CompileMath --> {3 x neg exp add}
( 3 * exp (sin 2)) CompileMath --> {3 2 sin exp mul}
( 3 * exp sin 2 ) CompileMath --> {3 2 sin exp mul}
(4 * - 7) CompileMath exec --> -28
(2^3) CompileMath --> {2 3 pow}
(5+3*2^3) CompileMath --> {5 3 2 3 pow mul add}
(5+3*2^3-4) CompileMath --> {5 3 2 3 pow mul add 4 sub}
(5+3*2^3/4) CompileMath --> {5 3 2 3 pow mul 4 div add}
(5+3*2^-3) CompileMath --> {5 3 2 3 neg pow mul add}
(4) CompileMath --> {4}
() CompileMath --> {}
(a=7+3) CompileMath --> {/a 7 3 add dup rolld Set}
(a=7+3;) CompileMath --> {/a 7 3 add dup rolld Set pop}
(a=7+3;6) CompileMath --> {/a 7 3 add dup rolld Set pop 6}
(a=7+4;b=2*exp(-2.0/10)) CompileMath --> {/a 7 4 add dup rolld Set pop /b 2 2.0 neg 10 div exp mul dup rolld Set}
(Function({x+2},'x)) CompileMath --> {{x 2 add} /x Function}
(f=Function({x+2},'x)) CompileMath --> {/f {x 2 add} /x Function dup rolld Set}
(f={#+2}) CompileMath --> {/f {<< >> begin /# Set # 2 add end} dup rolld Set}
(f={#1-#2}) CompileMath --> {/f {<< >> begin /#2 Set /#1 Set #1 #2 sub end} dup rolld Set}
({#1-#2}) CompileMath exec --> {<< >> begin /#2 Set /#1 Set #1 #2 sub end}
([4,3,2]) CompileMath --> {[4 3 2]}
(x=7+[4,3,2]*2) CompileMath --> {/x 7 [ 4 3 2 ] 2 mul add dup rolld Set}
([]) CompileMath --> {[]}
(<< 'x : [-3, 9]*2, 'y : 7 >>) CompileMath --> {<< /x [ 3 neg 9 ] 2 mul /y 7 >>}
(<< >>) CompileMath --> {<< >>}
(5+3 // Function( {2*x+1},'x) ) CompileMath exec --> 17
(1+(5+3 // Function( {2*x+1},'x)) ) CompileMath exec --> 18
( [ 3, [ 2, 1], -9] // Flatten) CompileMath exec --> [3 2 1 -9]
( [ 3, [ 2, 1], -9] // Flatten // {Select(#,{#<3})} ) CompileMath exec --> [2 1 -9]
(5+3 // {#+1} ) CompileMath exec --> 9
(7 5 // {#1-#2}) CompileMath exec --> 2
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| Bugs: | The present version fails for doubles with negative exponents because the lexer just replaces all "-" with /sub. A slightly smarter lexer using a regular expression can solve this problem. | ||
| Remarks: | The function can be improved by using a more powerful parsing scheme. The predictive recursive parsing scheme is used here as an educational example. | ||
| Author: | Diesmann | ||
| FirstVersion: | 090117 | ||
| References: | [1] The Dragon Book, 1988, chapter 2 | ||
| Source: | /home/abuild/rpmbuild/BUILD/nest-2.4.1/lib/sli/mathematica.sli |
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